5.
UPSI student make visited to 2 river They found that one of thearound Tg. Malim to complete their river polluted and more fish task in doing exp. To study the died . sample of river of water So they took the The other river sample of the river and In your opinion has clean and study the content of why fish died?? clear water. the water.

6.
Higher BOD, means that there is dissolvedoxygen in the water, as aerobic bacteria uses up nearly all of it for respiration.Hence less dissolved oxygen available for the fish to use for respiration, So fish will died.

7.
From your observation what is deferencebetween river A and river B?Which water has low content of theoxygen ? why??

9.
PROCEDURE1. 5 beaker were labelling with A, B, C, D and E.2. 100 mL of pond water are collected and pour into beaker A.3. *The D.O probe was placed in the beaker A to read the initial D.O concentration directly.4. The result were recorded in Data Logger Spreadsheet Program.5. Steps 1 to 4 were repeated by using different samples of water which are drain water, distilled water, aquarium water and pipe water which the samples of water is poured into beaker B, C, D and E respectively.

10.
6. The samples were let until 5 days and D.O probes was placed again in these samples to read the final D.O concentration.7. BOD value was determined by the following formula: B.O.D value = Final D.O – Initial D.O p*Note that, before put the sensor into the next sample of water, rinse the sensor with distilled water.

12.
• The blue line represents drain water. The red line represents aquarium water. The pink line represents pond water. The green line represents pipe water. The last purple line represents distilled water. This graph shows the BOD (Biological Oxygen Demand) level of the water sample against time.• Graph shows the drain water have the highest BOD level which is 0.963mg/l. While, the lowest BOD level is distilled water which have 0.42 mg/l.• This shows that the most polluted water sample is drain water followed by aquarium water sample, pond water, pipe water and the less polluted water sample is distilled water.

14.
• The very important thing to know is the dissolve oxygen (DO) content of the sample to measuring the BOD of a water sample. The amount of DO in water affects natural biochemical processes in two ways where by limiting the amount of oxygen available for respiration and by affecting the solubility of essential nutrient in the water sample. The decomposition of organic matter is the greatest factor in the depletion of available oxygen in water body. As the organic content in water increase, there is a corresponding increase in bacterial activity and decrease the dissolved oxygen content.• The microorganisms such as bacteria are responsible for decomposing organic waste. When the organic matter such as dead plants, leaves, grass clippings, manure, sewage, and food waste also present in a water supply. This will support the bacteria to begin process of breaking down the waste. This situation can cause more available dissolve oxygen was consumed by aerobic bacteria, robbing other aquatic organisms that need oxygen to live.• If there is a large quantity of organic waste in the water supply, there will also be a lot of bacteria present working to decompose this waste. In this case, the demand for oxygen will be high in the water sample due to the bacteria will cause the BOD level will be high. As the waste was consumed or dispersed through the water sample, BOD level will begin to decline.

15.
• As the BOD level is high, dissolved oxygen (DO) level will decrease because the oxygen available in water is being consumed by microorganisms in the water. Since less dissolved oxygen is available in the water, organisms such as fish, caddisfly larvae and mayfly nymphs and other aquatic organisms cannot survive. This will cause the aquatic organisms become extinct over the time. At high BOD levels, organisms such as macroinvertebrates that are more tolerant of lower dissolved oxygen such as leeches and sludge worms may appear and become numerous.

16.
• NOTE: Generally, when BOD levels are high, there is a decline in DO levels. This is• because the demand for oxygen by the bacteria is high and they are taking that oxygen from the oxygen dissolved in the water. If there is no organic waste present in the water, there wont be as many bacteria present to decompose it and thus the BOD will tend to be lower and the DO level will tend to be higher.• At high BOD levels, organisms such as macro invertebrates that are more tolerant of lower dissolved oxygen (i.e. leeches and sludge worms) may appear and become numerous. Organisms that need higher oxygen levels (i.e. caddisfly larvae and mayflynymphs) will NOT survive.